1. Field of the Invention
The invention relates to a magnetic structure for generating magnetic fields to be used in nuclear magnetic resonance image detection, and in particular having means for generating a magnetic field with the characteristics required to obtain valid images inside a predetermined tridimensional area,
2. Description of Related Art
Prior art magnetic structures may be substantially of two types, i.e. magnetic structures using permanent magnets, or magnetic structures using electromagnets either of the resistive or of the superconductive type. These structures are used both for total body image detection, in which the body under examination is substantially completely inserted inside the magnetic structure, and for the detection of particular target zones, like specific limbs, or else.
In order to obtain valid images through the use of nuclear magnetic resonance, the magnetic field must have certain characteristics, namely in intensity and homogeneous distribution, at least in the volume being meant to receive the body or the part thereof to be examined. Unless a homogeneous distribution, within predetermined tolerances, is reached, the image obtained by spin echoes is of no use, since it does not correspond accurately to real conditions.
In order to provide magnetic fields having the characteristics required to obtain valid, i.e. useful nuclear magnetic resonance images, prior art magnetic structures are of considerable size. Hence, said structures are heavy, uneasy to handle, and expensive, not only per se, but also due to the consequences on the whole structure of the apparatus.
This drawback is notably more serious in case of magnetic structures for the examination of particular parts or zones of the body, which require a higher handleability and also a lower cost.
Further magnetic structures are currently known, of the so-called open type, having apertures for access to the volume being meant to receive the body or the part thereof to be examined, on at least three sides, and having substantially C- or U-shaped conformations. Although these known structures allow for an easier access, they do not solve the handleability and space requirement problems. To obtain the desired and necessary magnetic field characteristics, the magnetic structures must have a huge size, so that the field distortion areas along open sides may be kept as far as possible, whereas the possible means for compensating distortions are substantially of the passive type, and are not sufficient to allow for a dimensional contraction of the structures.